Effect Of Substrate Types On Oyster Settlement,Growth,Population Establishment And Reef Development

Oyster reef is known as the " coral reef " in temperate regions,which has important ecological functions in the purification of water body,providing fish habitat and the maintenance of biodiversity.Due to the influence of natural disasters and man-made factors,the area of the natural oyster reef has decreased gradually.At present,the restoration of oyster reef is one of the important means to maintain the coastal fishery resources and to repair the coastal water ecosystem.The most commonly used substrate of oyster reef restoration is oyster shell,but its resources shortage restricts the largescale implementation of oyster reef restoration project,so screening alternative substrates suitable for the growth of oyster larvae has become one of the key technologies to solve the urgent need in the restoration of oyster reef.Both field observation and indoor experiment showed that substrate including calcium has significant effects on settlement of oyster larvae.But at present,the academic still don’t know the mechanism of calcium on the settlement of oyster larvae,and whether is there a significant difference of calcium in different forms in substrate of artificial reefs on the settlement of oyster larvae? Is the higher the calcium content in substrate,the better the effect of the induction effect on the settlement of oyster larvae? Is there threshold of induced effect? In this regard,we examines these hypotheses by the following three experiments.Experiment 1: Effect of calcium form in substrate on spat settlement of Pacific oyster Crassostrea gigasTo understand whether calcium in different forms in substrate of artificial reefs could affect oyster spat settlement,we designed an experiment with calcium in different forms and concentrations,and oyster larvae abundances in seawater in threefactor randomized manner.The density and shell height of spats attached onto substrate were measured.Results show that calcium concentration(10%,60%)showed no significant effect on the density and shell height(P>0.05).However,both calcium forms and planktic larvae abundance affected significantly the density and shell height of settled oyster spat in substrate(P<0.05).The order of impact of three calcium forms on the settlement was organic calcium > carbonate calcium = sulfate calcium in an identical oyster larvae abundance in seawater,while for the shell height,the order was opposite.The density of oyster spat settled was greater in high abundance of oyster larvae than in low abundance(P<0.05)regardless of calcium forms.Therefore,organic calcium could induce the settlement of oyster larvae significantly.Experiment 2: Effect of calcium carbonate content in substrate on spat settlement of Pacific oyster Crassostrea gigasTo understand whether calcium content in substrate of artificial reefs could affect oyster spat settlement,we designed a two-factor randomized experiment with calcium carbonate in different contents(four treatment levels: 5%,20%,40%,60%)and oyster larvae abundances(low treatment group: 1 ind?m L-1,high treatment group: 7–8 ind?m L-1).The density and shell height of oyster spats attached onto experimental substrates were measured.Results show that both calcium content and planktic larvae abundance significantly affected the density of settled oyster spats(P<0.05).Planktic larvae abundance in seawater had a significant effect on the shell height of settled oyster spats(P<0.05),but calcium content did not significantly affect the shell height of settled oyster spats(P>0.05).The substrate with calcium carbonate content of 20% showed the greatest inducing ability to settlement of oyster larvae,and attracted significantly greater oyster settlement than the experimental group of 60%(P<0.05).The density of settled oyster spats was greater in the high abundance of oyster larvae than in the low abundance(P<0.05)regardless of calcium carbonate content,while the contrast result was found for the shell height: high larval abundance treatment < low larval abundance treatment(P<0.05).Experiment 3: Effects of Substrate Types on the Development of Oyster ReefSuccessful and sustainable oyster reef restoration relies on suitable substrate material that is both readily available and encourages long-term recruitment and growth of oysters.China is increasing oyster reef restoration,however,little information is available to guide sustainable practices under local conditions and on ecologically relevant time scales.This study examines the effects of four substrate materials(oyster shell,clam shell,limestone,and clay brick)on community demographics for the Kumamoto oyster(Crassostrea sikamea)and associated macrofauna over a 3-year period in Xiangshan Bay,China.During the first two years,oyster and clam shell had similarly high recruitment and abundance of live oysters when compared to limestone and clay bricks.All substrate types,however,ended up with similar oyster abundances and size distributions after 3 years.Similar trends existed with regard to structural complexity(weight and volume)of substrate and any differences at the onset of the experiment were no longer apparent by the end.Abundance and community structure of associated macrofauna did not differ among the four substrate types regardless of time.These results indicate that different types of substrate material may be used for oyster reef restoration in China given projects have a scope longer than 2 years.These restored reefs can be expected to support viable and self-sustaining oyster populations with increased structural complexity and vibrant macrofaunal communities.Restoration practitioners using the Kumamoto oyster in China may utilize local materials as substrate for reefs and look forward to success where oyster recruitment is adequate and other factors such as predation and sedimentation are low.The research results have important theoretical and practical significance for the selection of alternative substrate materials in the restoration of oyster reefs and oyster culture,thus providing theoretical basis for the design and implementation of the restoration project of oyster reef.